DESCRIPTION; This application requests support for a Keystone Symposia meeting entitled The Microbiome, organized by Andrew T. Gewirtz, Fergus Shanahan and Ruth E. Ley, which will be held in Keystone, Colorado from March 4 - 9, 2012. Emerging themes from several traditionally disparate areas of research have begun to coalesce around the concept that the complex microbial communities that inhabit most external human surfaces play a key role in health and disease. Specifically, processes including basic immune system development, host- pathogen interactions, metabolic disease, and cancer are all greatly influenced by the composition and bioactivity of the microbiota that lives within us. Understanding how mammalian hosts regulate their microbiota and the myriad of ways by which the microbiota can alter susceptibility to a wide range of diseases is a key opportunity to better understand numerous diseases and, subsequently, provide strategies to promote human health. Thus, the goal of the Keystone Symposia meeting on The Microbiome is to facilitate the understanding of mechanisms that maintain a healthy host-microbiota relationship and explore how perturbations in this relationship increase susceptibility to a variety of diseases, especially those associated with chronic inflammation. Opportunities for interdisciplinary interactions will be significantly enhanced by the concurrent meeting on Innate Immunity: Sensing the Microbes and Damage Signals, which will share a keynote address and three plenary sessions with this meeting. PUBLIC HEALTH RELEVANCE: Numerous human diseases - especially the many diseases associated with inflammation - have been shown to be associated with alterations in the vast and diverse populations of microbes that populate most external human surfaces. Participants at the Keystone Symposia meeting on The Microbiome will gain a greater understanding of the mechanisms by which the mucosal immune system and microbiota influence each other and how disturbances in their normal relationships result in disease. Opportunities for interdisciplinary interactions will be significatly enhanced by the concurrent meeting on Innate Immunity: Sensing the Microbes and Damage Signals, which will share a keynote address and three plenary sessions with this meeting.